1. Field of the Invention
The present invention relates to image processors which process input image data to obtain a resultant image having a desired magnification(s) in a horizontal and/or vertical scanning direction(s) with respect to an original image and more particularly, to an image processor in which input image data is enlarged with a predetermined magnification(s) in a horizontal and/or vertical scanning direction(s) and thereafter the image data is reduced, whereby the need for provision of a memory for speed conversion can be eliminated with its simplified and small-scaled arrangement.
2. Description of the Related Art
In general, as an image processor which processes input image data to obtain an image having a desired magnification(s) in a horizontal and/or vertical scanning direction(s) with respect to an original image, there is known an image processor which performs interpolating operation over input pixel data to realize an image enlarged in the horizontal scanning direction or which performs interpolating operation over input line data to realize an image enlarged in the vertical scanning direction.
Further, when it is desired to read a two-dimensional image with use of a one-dimensional reading sensor, such a method is generally employed that a relative position between the one-dimensional reading sensor and the image is moved in a direction (vertical scanning direction) perpendicular to the one-dimensional reading sensor and an original document to perform raster scanning operation.
With such a document stationary type image processor (which is also known as a flat bed scanner or a book reading scanner), for the purpose of avoiding its feeding irregularity, the one-dimensional reading sensor is moved at a constant speed in the direction perpendicular to the original document to realize raster scanning operation.
FIG. 11 shows a prior art image processor which performs interpolating operation over pixel data of input image data to obtain an output image corresponding to an original image but enlarged in a horizontal scanning direction. In the image processor of FIG. 11, an original image is raster scanned through a charge coupled device (CCD) 11 as a one-dimensional reading sensor to obtain an image, the image signal is converted at an analog-digital (A-D) converter 12 into digital image data that comprises continual n-bit pixel data for respective pixels, the digital image data is once input to a memory 15 for speed conversion, the image data stored in the memory 15 is read out under control of an interpolating circuit 16, and the read-out image data is subjected to an interpolating operation of inserting predetermined pixel data to thereby obtain image data enlarged in the horizontal scanning direction (raster direction).
In this case, the interpolated pixel data is determined by referring to pixel data therearound to be interpolated. For example, the pixel data indicative of the previous pixel read out from the memory 15 is used as interpolation pixel data as it is.
FIG. 12 shows a relationship between the output image data of the A-D converter 12 and the output image data of the interpolating circuit 16 in the prior art image processor of FIG. 11. In more detail, the A-D converter 12 sequentially outputs n-bit pixel data PD1, PD2, PD3, PD4, . . . corresponding to continual pixels as shown in Part (a) of FIG. 12. When it is desired to doubly enlarge the image date at a position of the pixel data PD2, the same pixel data PD2' as the pixel data PD2 is inserted between the pixel data PD2 and PD3 as shown in Part (b) of FIG. 12. In this case, the subsequent pixel data PD3, PD4, . . . must be delayed with respect to the read-out image data.
Since the CCD 11, which usually comprises a one-dimensional reading sensor, can be moved only at a constant speed, the prior art image processor requires provision of such a memory 15 as a RAM for storing at least one line of image data for speed conversion, as shown in FIG. 11.
FIG. 13 shows another prior art image processor which performs interpolating operation over input image data with respect to its line data to enlarge an original image in a vertical scanning direction. In this example, an output image signal of a CCD 21 when line scanning an original image for its reading is converted at an A-D converter 22 into n-bit digital image data, the image data is read out usually on every line basis, so that, when the reading of one line of the image data is completed, a scanner motor 25 is controlled under control of a scanner controller 24 to move the CCD 21 in the form of one-dimensional reading sensor by an amount corresponding to one line in a direction perpendicular to an original document. When it is desired to interpolate predetermined image data (line data) on every line basis for the purpose of enlarging the dimensions of the image in a vertical scanning direction, speed conversion becomes necessary. To this end, the n-bit image data as the output of the A-D converter 22 is once stored in a page memory 27, the image data is later read out from the page memory 27 under control of the scanner controller 24 and then sent to an interpolating circuit 26 to be subjected therein to an interpolating operation of inserting predetermined image data on every line basis. At this time, the line data to be inserted is determined by referring to the line data before and after that line data. For example, the line data of the previous line is used as interpolation line data as it is.
For example, in the case where it is desired to doubly enlarge the continual image data of lines L1, L2, L3, L4, . . . as shown in FIG. 14 at the position of the line L2, when a line L2' having the same image data as, e.g., the line L2 is inserted into between the lines L2 and L3, the subsequent lines L3, L4, . . . must be delayed with respect to the read-out image data.
When raster scanning is carried out by moving the one-dimensional reading sensor at a constant speed in a direction perpendicular to the original document, the subsequent lines L3, L4, . . . cannot be delayed with respect to the read-out image data. To avoid this, such an arrangement is required that the page memory 27 for storing at least one page of the read-out image data is prepared so that the read-out image data is once stored in the page memory 27 for speed conversion.
As has been explained above, the prior art image processor has had such a problem that, when it is desired to obtain an image enlarged in the horizontal scanning direction (raster direction), the enlarging operation requires the interpolating operation of the image data and thus at least such a line memory as a random access memory (RAM) for the interpolating operation is required; whereas, when it is desired to obtain an image enlarged in the vertical scanning direction, the enlarging operation requires the interpolating operation of the image data and thus at least such a page memory for once storing at least one page of image data is required, which results in its complicated arrangement and control.